This invention relates generally to touch sensitive systems, and more particularly to touch panels that detect surface acoustic waves (SAW).
Touch sensitive systems are used to provide two-dimensional coordinate information. One example may be an opaque track pad while another example may be a transparent touch panel placed in front of a display such as a liquid crystal display. Touch sensitive systems are used in many different applications, including small hand-held devices such as phones, cameras and personal digital assistants, and including larger desktop applications such as touch systems for restaurants, banks and automated teller machines, museums and the like.
Conventional SAW touch panels have a number of limitations including vulnerability to false activations from liquid contaminants, and lack of response to a pointed stylus. As the marketplace finds value in the detection of more than one simultaneous touch, such as with two finger zoom gestures, the inherent multi-touch capabilities of SAW become more attractive. However, with conventional SAW touch panels two finger gestures with fingernail touch contact are not supported. In the past a layered SAW coversheet with an exterior load-spreading layer and an interior compliant layer has been proposed to address these issues. However, known SAW coversheet designs force an undesirable trade-off between touch sensitivity and the need to avoid sticking failures, wherein the compliant layer does not immediately release from the substrate when a touch is removed. There is an unmet need for a SAW coversheet solution that provides a desired level of touch sensitivity without the aforementioned sticking problem.